A cost-effective method of shipping and storing dry bulk products is to use a large bulk bag, known in the industry as a flexible intermediate bulk container (FIBC). FIBCs eliminate the need for pallets and elaborate packaging and unitizing equipment. Such bulk bags are generally made of plastic fabrics (although burlap and kraft paper are also used). Woven polypropylene is preferred for its low cost and high strength. Nylon or polyester webbing is used to add strength and, with most designs, to serve as sling loops for carrying the bulk bag by fork-lift trucks or suspended by a crane for ship-loading. In those instances where fine particulate material is to be stored, an inner bag liner formed of a plastic such as 1 to 4 mil polyethylene is specified to contain the finer particulates and to protect the product from moisture or contaminates.
Capacities of FIBCs can vary, ranging anywhere from 20 cubic feet to 200 cubic feet. However, most bags are about the same size as a typical pallitized unit load and, when filled, will weigh about one ton. This enables most shippers and users of FIBCs to handle them with existing in-plant equipment such as fork-lift trucks, jib cranes or overhead cranes.
Bulk bags come in a variety of constructions, usually top-filled and bottom discharge although a variety of fill and discharge arrangements are known in the art. Typically, a bulk bag having a discharge spout at its bottom is from ten or fifteen inches in diameter and one to two feet in length. A tie-off/shut-off cord on the shoot is provided at the base of the bag. Once the bag and the bottom discharge shoot is positioned over the container or conduit in which the material is to be emptied, undoing the tie-off cord provides a means for quick release of the material. In many instances, the discharge of the material occurs as the bag is being held by a fork-lift truck or an overhead crane while the bag is opened by an operator therebeneath over a cone-shaped hopper, blender or other container of some sort. After the bag is opened, it is then lowered down into the cone or receiving spout to empty.